The development of a new type of oxygenator is proposed utilizing a new concept of blood oxygenation based on the encapsulation of gas bubbles within a thin film of inert fluorochemical, thus avoiding a blood-gas interface but allowing adequate gas transfer. The encapsulated bubbles are passed countercurrent to the blood flow. Oxygen passes through the liquid membrane into the blood and carbon dioxide takes the reverse course. The bubbles emerge from the blood phase and collapse, releasing carbon dioxide. The fluorochemical is reused. Prior experimentation has demonstrated the feasibility of this method. In vivo and in vitro experiments have been designed to study the biocompatibility and the physicochemical properties of these fluorochemicals. A prototype oxygenator would undergo in vitro and in vivo testing. It is hoped that this liquid membrane oxygenator will allow long-term extracorporeal blood oxygenation. Our efforts in the development of the oxygenator quickly made it clear that it is important to understand the physical and biological interactions of fluorochemicals with blood. This information is not only essential in the development of a reliable safe oxygenator for clinical use but is invaluable in the development of fluorochemicals for other medical applications. For these reasons, we are proposing to investigate the biological tissue fluorochemical interface in a controlled, systematic manner.